Composite components are frequently produced using radically crosslinkable polymer compositions based on, for example, unsaturated polyester resins (UP resins). Unsaturated polyester resins are obtainable by polycondensation of dicarboxylic acids or dicarboxylic anhydrides, some of which at least carry ethylenically unsaturated groups, with polyols. The radically crosslinkable polymer compositions further comprise monomers having ethylenically unsaturated groups, generally styrene. Styrene is added to the radically crosslinkable polymer compositions, for example, in order to dissolve the crosslinkable polymers and to ensure that the radically crosslinkable polymer compositions are fluid materials. As further constituents, the radically crosslinkable polymer compositions often further comprise fiber materials such as glass fibers, carbon fibers or corresponding fiber mats (Fiber Reinforcing Plastic composites=FPR composites), which lead to reinforcement of the composite components obtainable by curing the radically crosslinkable polymer compositions.
A problem associated with the processing of such radically crosslinkable polymer compositions to composite components is the volume contraction in the course of curing of the polymer compositions. In order to reduce the contraction that accompanies curing, therefore, additives known as low-profile additives (LPAs) are added to the radically crosslinkable polymer compositions. Low-profile additives reduce the contraction on curing, relieve inherent stresses, reduce the formation of microcracks, and facilitate compliance with manufacturing tolerances. The low-profile additives are typically thermoplastics such as polystyrene, polymethyl methacrylate, and, more particularly, polyvinyl acetate, and frequently also contain carboxyl-functional comonomer units. Thus, for example, U.S. Pat. No. 3,718,714 or DE-A 102006019686 recommend copolymers based on vinyl acetate and ethylenically unsaturated carboxylic acids as LPAs for the production of composite components based on unsaturated polyester resins.
Conventional LPAs hence consist of petrochemical products. Increasingly, however, LPAs based on renewable raw materials are being called for. Nevertheless, many of the existing products based on renewable raw materials are expensive, incompatible with ethylenically unsaturated monomers, such as styrene, or show no LPA effect.
Against this background, the object was to provide polymers based on renewable raw materials which act as low-profile additives (LPAs) but do not have the aforementioned disadvantages. The LPAs, furthermore, ought if possible to lead to composite components having performance properties, such as mechanical properties, for example, like those also achieved with conventional LPAs.
The object has been achieved, surprisingly, through use of polymers based on renewable raw materials, obtained by radically initiated polymerization of ethylenically unsaturated monomers in the presence of renewable raw materials selected from the group encompassing carbohydrates and natural rubbers.
Polymers based on ethylenically unsaturated monomers and renewable raw materials are known per se, as described for example in DE-A 2742595, U.S. Pat. No. 3,640,925, WO 90/09406, WO 94/00514, DE-A 19619680, U.S. Pat. No. 5,583,193, US 2006/0003014 or WO 93/11300. Not known, in contrast, is the use of such polymers as LPAs.